Fix a memory leak with pending jank classifications

If the front of the pendingJankClassification deque is
stuck(FrameTimeline never received it) for some reason, the current
logic never releases it and the deque keeps growing in size until the
layer itself is destroyed. This has resulted in some memory leaks
recently.

Bug: 181328447
Test: heap_prof trace
Change-Id: If71225f52da3bbd9b0b0d46af75f933fd48d5bd5